Rotatable reflector for cinematograph cameras



y 9, 1950 c. VlNTEN 2,506,909

ROTATABLE REFLECTOR FOR CINEMATOGRAPH CAMERAS Filed Dec. 8, 1948 A itorn e y Patented May 9, 1950 RQ' T TAB E R LECTOR, FO QINEMTATO? GRAPH CAMERAS Charles Vinten, London, England Application December 8, 1948, Serial No. 64,083 In Great Britain December- 24, 1947 2 Claims. 1

This. inventionrelates to rotatable reflector for cinematograph cameras, and more. especially to cameras andother equipment provided with rotatable reflector device such as described in the specification of U. S. A. Patent application No. 746,732flled on May 8, 1947., now Patent No. 2,498,188 issued February 21, 1950.

The invention is concerned with the construction of the aforesaid rotatable reflector element, and aims at providingan effective mounting for such a device in the apparatus, and a method of manufacture which will achieve the desired result in a simple and efflcientmanner,

The invention accordingly consists in a rotatable reflector element, e. g. for use in a'cinematographic camera, having an optically finished reflecting surface. on one face accurately perpendicular to the rotational axis of the element, and a substantial portion of its opposite face'accurately finished in relation to the reflecting surface, to form a bearing surface for the element during its rotation.

The element may conveniently be in the form of a disc with the reflecting surface on its top face, and having on its under face a bearing or mounting surface truly parallel to the reflecting surface. Alternatively or in addition the sides of the undersurface of the element may be of conical, spherical or other suitable shape of prearranged angle in relation to the reflecting surface, and properly aligned relatively thereto. The element is mounted in a. supporting member having bearing surfaces prepared to receive the rear and/or side wall bearing surfaces abovementioned, thus ensuring that the reflector element is properly supported during rotation, and prevented from fiexural or other vibration.

The invention will be clearly understood from the following description of one form (given, however, merely by way of example) which it may assume, and this description will be more readily followed by reference to the accompanying drawings wherein:

Figure 1 represents a plan view of a reflector element for a cinematographic camera according to the invention;

Figure 2 represents a side sectional View along the line AA of Figure 1; and

Figure 3 represents a side sectional view along the line B-B of Figure 1.

In carrying the invention into effect in one convenient manner and referring to the accompanying drawings, a reflector element for a cinematographic camera or like apparatus (such as described for example in the specification of U.

S. Patent application No. 746,732) may be prepared from a single block of mild steel or other suitable metal. This block is first turned to circular disc shape of say, approximately 5%,, inches diameter and /2 inch or less thick. In its final form the element comprises a circular central body portion I with two symmetrically disposed arcuate annular peripheral flanges 2, 3, projecting therefrom, each extending rather less than round the body periphery. The radial width of these flanges may conveniently be, say, ratherless than one inch, and after the turning operation abovementioned the disc may be milled in order to remove the unwanted peripheral portions of the block between the flanges, thus converting the block approximately to its final outline shape in plan, corresponding substantially to the view shown in Figure l herewith.

The disc I is thereafter jig-drilled, during which operation, in order to reduce weight, part of the upper surface of the central body portion of the disc (to about half-thickness of the disc) may be removed leaving a recess 4 forming the disc into a dish-shaped element. A central aperture 5 to receive a driving shaft may also be drilled, and four screw holes 6, symmetrically disposed about the central aperture 5 and at suitable distance therefrom, provided for securing the disc to its driving means. Any other apertures and/ or recesses necessary in the body portion of the disc, e. g. arcuate-slots I, may be drilled at the same time.

After drilling, the front peripheral flange surfaces 2, 3, and at least part of the rear surface of the disc as at Sam ground to approximate planeness and parallelism. If desired, (and preferably), the undersurface 9 of the peripheral flanges 2, 3, are formed of conical shape, as shown, so that the flanges narrow to their outer edges Where they may be provided with a narrow 45 chamfer, also as shown. Care should be taken to ensure that the axis of these conical surfaces is perpendicular to the plane of the front flange surfaces.

After this initial grinding the front surfaces 2, 3, of the peripheral flanges of the disc are provided with a hard chrome plating and all other surfaces are gun-blacked, whereafter the hard chrome plating of the flanges is again ground to a plane surface. The disc is thereafter brought to approximate static and dynamic balance about its rotational axis, metal being removed from appropriate parts of the disc body, e. g. from the slots 1, when and where necessary, for that purpose.

The front faces of the peripheral flanges (which form the ultimate reflecting surfaces of the device), are next optically polished, by any convenient known treatment.

The next step in manufacturing the rotatable reflector (being an important step in accordance with the present invention) consists in accurately grinding the mounting surface or surfaces, 8, 9, of the device by reference to the polished optical surfaces 2 and 3 abovementioned. The mounting surface 8 may be formed on the rear face of the body portion I of the disc, and in this case this rear surface is accurately ground to be parallel to the optical surfaces. Alternatively, or in addition, the conical or spherical surfaces 9 at the periphery of the disc on its rear face may be employed as mounting surfaces, and in this case these conical or spherical surfaces are accurately ground to the desired conicity or sphericity, and

with their axis perpendicular to the plane of the optical surfaces 2, 3. These accurate grinding operations, are carried out by reference to the polished optical surfaces 2, 3, and are designed to ensure that the reflecting surfaces 2, 3, and the rotational axis of the element will be accurately perpendicular to one another.

The final steps in manufacturing a rotatable reflector according to the invention consist in effecting final and accurate static and dynamic balance of the disc about its rotational axis, and aluminising the polished optical surfaces 2 and 3, whereafter the reflector is ready for installation in a cinematographic camera or other apparatus.

In order to ensure proper tempering of the metal and elimination of unwanted distortion and strain, the initial block is slowly annealed after rough machining, and long periods of time allowed to lapse between the various machining operations to which it is subjected as described above. As far as possible it should also be kept during its period of manufacture at a substan- ,system thereof, its bearing surface provides flrm faces.

support for the reflecting surfaces during their rotation, and eliminates all possibility of flexural or other vibration of the reflector element liable to mar the specular reflection characteristics of the reflecting surfaces.

It will be noted that important features of the invention consist in the provision, on a rotatable reflector of the kind contemplated, of 'a large, accurately finished bearing of mounting surface or surfaces on a face of the disc opposite, or substantially opposite, to the reflecting surfaces; and in the step, in manufacturing such a reflector, of grinding or otherwise finishing these bearing or mounting surfaces off the optically polished sur- Subject to the incorporation of either or both of these features, it should be understood that the invention is not limited solely to the constructional details of the form described above, or to the various manufacturing steps described, since these may be modified, in order to I carry the invention into effect under different conditions and requirements encountered, without departing in any way from the scope of the appended claims.

What I claim is:

1. A rotatable reflector element for use in a cinematographic camera comprising a rotatable metallic dish-shaped disc carrying two opposite radially-projecting arcuate annular metal flanges, achromium plated surface on said flanges, optically finished and aluminised to form accurate plane reflecting surfaces perpendicular to the rotational axis of said disc, and a smooth surface on the face of said disc opposite to said reflecting surfaces, accurately ground with reference to said reflecting surfaces to form a mounting surface for said disc.

2. A rotatable reflector according to claim 1 wherein the rear surface of said reflector comprises a central plane circular area accurately parallel to said reflecting surfaces, and a frustroconical surface surrounding said central area and accurately ground to provide additional mounting surface for said disc.

CHARLES VINTEN.

REFERENCES CITED The following references are of record in the file of this patent:

FOREIGN PATENTS Number Country Date 856,426 France Mar. 12, 1940 218,900 Switzerland Jan. 15, 1942 225,795 Switzerland Feb. 28, 1943 

